Installing AX 2012 with an SQL 2012 Database
If you want to take advantage of the new capabilities in Microsoft SQL Server 2012, you're going to have to do some extra work to get Microsoft Dynamics AX 2012 installed. There is a hotfix available now which allows you to get the install to go through - the hotfix is available on CustomerSource or PartnerSource as a Knowledge Base article - KB2680186.
When you get to the page on CustomerSource, click on the top of the screen where there's a link to "View and request hotfix downloads" - that will take you to a special support page where you can request the hotfix directly.
To install the hotfix, you'll need to do a "slip-stream" installation where you place the hotfix in an "Updates" folder on the installation directory (generally inside a folder labeled with the KB number). Setup will automatically detect the updates and add that code into the process, so you are able to use AX 2012 with SQL 2012.
For more information on the process of slip-streaming, check out this TechNet article: http://technet.microsoft.com/en-us/library/hh378076.aspx.